This invention relates to articles, particularly brass articles, having a multi-layered decorative and protective coating having the appearance or color of bronze, particularly antique bronze, thereon.
It is currently the practice with various brass articles such as faucets, faucet escutcheons, door knobs, door handles, door escutcheons and the like to first buff and polish the surface of the article to a high gloss and to then apply a protective organic coating, such as one comprised of acrylics, urethanes, epoxies and the like, onto this polished surface. This system has the drawback that the buffing and polishing operation, particularly if the article is of a complex shape, is labor intensive. Also, the known organic coatings are not always as durable as desired, and are susceptible to attack by acids. It would, therefore, be quite advantageous if brass articles, or indeed other articles, either plastic, ceramic, or metallic, could be provided with coating which provided the article with a decorative appearance as well as providing wear resistance, abrasion resistance and corrosion resistance. It is known in the art that a multi-layered coating can be applied to an article which provides a decorative appearance as well as providing wear resistance, abrasion resistance and corrosion resistance. This multi-layer coating includes a decorative and protective color layer of a refractory metal nitride such as a zirconium nitride or a titanium nitride. This color layer, when it is zirconium nitride, provides a brass color, and when it is titanium nitride provides a gold color.
U.S. Pat. Nos. 5,922,478; 6,033,790 and 5,654,108, inter alia, describe a coating which provides an article with a decorative color, such as polished brass, provides wear resistance, abrasion resistance and corrosion resistance. It would be very advantageous if a coating could be provided which provided substantially the same properties as the coatings containing zirconium nitride or titanium nitride but instead of being brass colored or gold colored was bronze, particularly antique bronze, colored. The present invention provides such a coating.
The present invention is directed to an article such as a plastic, ceramic, cermet or metallic article having a decorative and protective multi-layer coating deposited on at least a portion of its surface. More particularly, it is directed to an article or substrate, particularly a metallic article such as stainless steel, aluminum, brass or zinc, having deposited on its surface multiple superposed layers of certain specific types of materials. The coating is decorative and also provides corrosion resistance, wear resistance and abrasion resistance. The coating provides the appearance or color of bronze, particularly antique bronze, i.e. has a two-tone color: dark gray and dark yellow. Thus, an article surface having the coating thereon simulates a bronze, particularly an antique bronze surface.
The article first has deposited on its surface one or more electroplated layers. On top of the electroplated layers is then deposited, by vapor deposition such as physical vapor deposition, one or more vapor deposited layers. A first layer deposited directly on the surface of the substrate is comprised of nickel. The first layer may be monolithic or it may consist of two different nickel layers such as, for example, a semi-bright nickel layer deposited directly on the surface of the substrate and a bright nickel layer superimposed over the semi-bright nickel layer. Disposed over the electroplated layers is a strike layer comprised of a refractory metal or metal alloy such as zirconium, titanium, hafnium, tantalum or zirconium-titanium alloy, preferably zirconium, titanium or zirconium-titanium alloy. In one embodiment disposed intermediate the nickel layer and the strike layer is a strengthening layer comprised of chromium. Over the strike layer is a protective and decorative color layer comprised of a stack layer comprised of layers of carbon-rich refractory metal carbonitride alternating with layers of nitrogen-rich refractory metal carbonitride, such as zirconium carbonitride, titanium carbonitride, tantalum carbonitride and hafnium carbonitride, and the carbonitrides of refractory metal alloys, such as a titanium-zirconium alloy. These alternating layers of the stack layer may contain a small percentage of oxygen in order to increase the dark appearance of the coating. The small amount of oxygen ranges from about 2 to about 15 atomic percent. For zirconium, in the carbon-rich zirconium carbonitride layer, the carbon content generally is between about 25 to about 50 atomic percent, nitrogen content between about 5 to about 35 atomic percent, and this layer has a dark gray color. In the nitrogen-rich zirconium carbonitride layer, the nitrogen content is between about 25 to about 50 atomic percent, carbon content between about 5 to about 35 atomic percent; and this layer has a dark yellow color with a slight reddish tint. Neither of these two layers is thick enough by itself to make the coating have its own color. However, when two or more of these layers are present, the overall color of the stack layers mimics a dark gray and dark yellow two-tone antique bronze appearance. On the top of this color layer, a very thin layer of refractory metal oxide or refractory metal alloy oxide is deposited in order to improve the corrosion and chemical resistance of the coating.